This invention relates to diagnostic X-ray systems and more particularly to a system controlled in accordance with a digital computer having a plurality of selectable program instruction sets for completely controlling the operation of the system consistent with a particular inputted technique or procedure, operator inputs, inherent physical limitations of associated equipment, and various safety and legislated restrictions. It is a primary object of the present invention to provide a completely automated system of X-ray control whereby exposure optimization is effected in a sense of image quality, in particular resolution, and to maximize X-ray tube life.
X-ray tubes today are generally provided with two focal spot sizes, small and large, and are adapted to operate at two speeds, standard speed and ultra speed. It is also well known that X-ray image resolution is higher when the focal spot is smaller. Another thing which is known to effect image resolution is motion of the patient, either voluntary or involuntary, which causes blurring of the image. Examples of involuntary motion are those due to respiration, to the cardiovascular system, and to the digestive system. In order to minimize the deleterious effects of this type of motion on image quality, an attempt is made to keep the X-ray exposure time as small as possible. This, however, runs into conflict with the capability of the X-ray tube to withstand the relatively large amounts of heat dissipated. Generally this X-ray tube capability is expressed in the form of tube loading charts which are supplied by the X-ray tube manufacturer. In order to get the proper exposure of an X-ray film, the X-ray technique factors are selected largely by experience, but from a technical point of view in accordance with two rough guidelines. The first is the kilovoltage (kV) which has to be high enough to penetrate the subject, i.e. the photon energy must be high enough so that sufficient photons can exit from the patient in spite of absorption. Second the product of current expressed in milliamperes (mA) and time (s) expressed in seconds must be chosen long enough so that there is a sufficient number of photons passing through the patient in order to darken the film. As a rough guideline, film darkening is proportional to the product of mAs.times.kV.sup.n where n, for example, equals 4.
The following listing comprises prior art of which the applicant is aware:
U.s. pat. No. 4,035,648, Patel PA1 U.s. pat. No. 3,997,791, Winkler PA1 U.s. pat. No. 3,917,949, Winkler PA1 U.s. pat. No. 3,746,862, Lombardo, et al. PA1 U.s. pat. No. 3,838,285, Siedband, et al. PA1 U.s. pat. No. 3,968,372, Laughinghouse